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Nitella zamanii has been described and illustrated as a new species from a rice field at Charghat upazila in Bangladesh. The new species resembles Nitella furcata and N. polycarpa but differs by presence of accessory branchlets, spiky dactyls and size of oogonium, oospore and antheridium.DOI: http://dx.doi.org/10.3329/bjpt.v21i2.21358Bangladesh J. Plant Taxon. 21(2): 181-185, 2014 (December)

The light receptor and its mode of operation were studied in photosensitive oospores of Nitella furcata subsp. megacarpa (Allen emend. Wood). Brief pulses of light activated maximal germination of post-secondary dormant oospores removed from lake sediments. Fluence response data at 12 wavelengths were used to construct an action spectrum for germination. The shape of the action spectrum with its maximum at 669 nm provides evidence for the involvement of phytochrome. Germination was induced with photon fluences that established as little as 0.01% of the phytochrome in the far red-absorbing form, which suggests that phytochrome was operating in the very low-fluence response mode. The functioning of phytochrome in the very low-fluence response mode in Nitella is similar to that in higher plants.

Plasmodesmata were recorded in vivo in Nitella furcata using polarization and differential interference-contrast light microscopy, techniques that could prove useful for further physiological experimentation on intercellular transport in characean cells.Freeze-fractured, deep-etch replicas of Nitella endoplasm were prepared without the use of cryoprotective agents. The endoplasm, in which rapid cytoplasmic streaming occurs, contains intricate three-dimensional networks of filaments of which two prominent size classes are characterized: 7- to 8-nm putative actin filaments and 4- to 5-nm putative myosin filaments. It is quite likely that the putative actin filaments are components of the endoplasmic filaments, and that these filaments interacting with the 4- to 5-nm filaments produce the motive force generating the observed cytoplasmic streaming.

Oospores of Nitella furcata subsp. megacarpa (Allen emend. Wood) were collected from an oospore bank in the sediments of Lake George, New York. Incubated at constant temperatures, all or nearly all of the oospores germinated when exposed to a brief pulse of red light when the annual window of germinability was open. The window seems related to the annual cycle of sediment temperatures. It is open in spring and closes wit the onset of a secondary dormacncy in the summer. Oospores in storage follow a parallel path if held at 18°C, a summer equivalent temperature; the window remains open indefinitely if the oospores are held at 4°C. Attention is drawn to the similarity if the cyclic window of germinability in seeds of summer annuals and oospores of N. furcata.

SUMMARYThe present communication deals with a discussion on the significance of chromosome numbers in Charophyta. After presenting a brief review of the various views held on the basic chromosome numbers in the taxa of Chara, Nitella and Tolypella, the role of polyploidy in the evolution of Charophyta and the possible ways in which polyploid taxa might have originated in nature have been considered. On the basis of present evidences aneuploids seem to show restricted geographical distribution as compared to euploids. Maximum degree of polyploidy has been found to be prevalent in Chara zeylanica within the tribe Chareae and Nitella tenuissima and Nitella furcata within the tribe Nitelleae. Significance of polyploidy in relation to sex, taxonomy, external form, chromosome length, pH, and altitude has also been discussed with some specific examples.